The use of resistive coatings for arc suppression in cathode ray tubes is well known. It has been conventional practice in cathode ray tube construction to apply an electrically conductive coating on the interior surface of the funnel member of the tube envelope in a manner to extend from substantially the vicinity of the cathodoluminescent screen into the forward region of the adjoining neck member. This coating, which usually has a high positive electrical potential applied thereto via connective means traversing the wall of the funnel member, serves as a connective medium conveying a high electrical potential of substantially a common value to both the screen and the terminal electrode of the electron gun assembly oriented within the neck member of the tube envelope. Thus, the condition is present for the possible generation of a spark discharge between the terminal electrode and the adjacent lower voltage electrode in the gun assembly, especially in the presence of aggravating elements such as sublimation deposits, foreign particles, and minute projections extending into the inter-electrode spacings.
Arcing or dielectric breakdown within the cathode ray tube has always been an undesired possibility. The magnitude of the arcing has been found to sometimes exhibit destructive intensities of 100 amperes or more. With the increased employment of solid state components in television and allied display devices, arcing within the cathode ray tube can produce catastrophic effects on the vulnerable components in the externally associated operating circuitry. Additionally, an arc discharge initiated within the tube may seriously damage the internal structure thereof and resultantly promote leakage through the sublimation of deleterious metallic desposits on related surfaces in the region of the gun structure.
Cleanliness, precision, vigilance and care in the tube manufacturing process are ever continuing procedures employed to combat the materializing of conditions conducive for arcing. Nevertheless, human factors, processing sublimates, manufacturing tolerances and procedural variations may combine to produce an undesirable and aggravative situation.
Another technique for suppressing arcs in cathode ray tubes was suggested by Kabori et al. at an IEEE Conference on Consumer Electronics in Chicago on June 19, 1980. Kabori et al. used resistors made from Al.sub.2 O.sub.3 and clay with the addition of several weight percent of carbon for suppressing arcs in cathode ray tubes. The Al.sub.2 O.sub.3, clay and carbon is mixed, formed into a cylinder and then fired at approximately 1300.degree. C. in a reducing atmosphere to sinter and densify. The cylinder is then placed in an oxidizing atmosphere at a higher temperature. By controlling the firing time, the outside portion of the cylinder is oxidized and a ceramic sheath is formed.
In a Japanese patent application Public Disclosure No. 86055/1980 of Kabori et al., two kinds of resistances were described. One is a fixed body resistance using metal oxide, silicon or carbon as an electric conduction material to mix and form with the necessary material to create a ceramic, and then sintered at high temperature. Another is a thin film resistance using carbon, iron oxide, or silicon carbide (SiC) which is deposited inside the conduction film. It is made into the shape of a lead wire as a thin film resistance.